To manufacture batteries having a large energy density, research is presently being done on lithium-sulfur battery technology (in short: Li/S). If the cathode of a lithium-sulfur cell were made completely of elemental sulfur, an energy content of greater than 1,000 Wh/kg could theoretically be achieved. However, elemental sulfur is neither ionically nor electrically conductive, so additives must be added to the cathode, which significantly reduce the theoretical value. In addition, elemental sulfur is conventionally reduced during the discharge of a lithium-sulfur cell to form soluble polysulfides Sx2−. These may diffuse into areas, for example, the anode area, in which they may no longer participate in the electrochemical reaction of the following charge/discharge cycles. In addition, polysulfides may be dissolved in the electrolyte, which may not be reduced further. In practice, the sulfur utilization and therefore the energy density of lithium-sulfur cells is presently significantly lower and is currently estimated to be between 400 Wh/kg and 600 Wh/kg.
With regard to lithium-sulfur cells, Nazar et al. in Nature Materials, Vol. 8, June 2009, [pp] 500-506 describe that carbon nanotubes promote retention of polysulfides in the cathode chamber and ensure sufficient electrical conductivity at the same time.
Wang et al. describe in Advanced Materials, 14, 2002, No. 13-14, pp 963-965 and Advanced Functional Materials, 13, 2003, No. 6, pp 487-492 and Yu et al. describe in Journal of Electroanalytical Chemistry, 573, 2004, [pp] 121-128 and Journal of Power Sources 146, 2005, [pp] 335-339 another technology in which polyacrylonitrile (in short: PAN) is heated with an excess of elemental sulfur, the sulfur, on the one hand, being cyclized, while forming H2S polyacrylonitrile, to form a polymer having a conjugated π-system and, on the other hand, being bound in the cyclized matrix, in particular via sulfur-carbon bonds.